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Propagation model may help police quiet zone while boosting access to wireless services

The National Radio Quiet Zone, established in 1958, covers approximately 13,000 square miles of land spanning the border between Virginia and West Virginia.

An ECE propagation model that incorporates variations of terrain may provide the precision needed to improve both the protection of the National Radio Quiet Zone (NRQZ) and residents’ access to wireless services.

The NRQZ spans a region in West Virginia and Virginia that surrounds the Green Bank National Radio Astronomy Observatory (NRAO). Radio signals that could cause interference to the radio telescopes are considered illegal — including wireless Internet networks that leak outdoors and even cellular phone service to a ski resort.

Improved propagation models would enable better predictions of interference, possibly leading to some relaxation of limits in specified locations, according to Gary Brown, director of the ElectroMagnetics Interactions Laboratory (EMIL). “With more accurate models, those policing the quiet zone may be able to allow more powerful signals in certain situations.” The EMIL team recently developed a computationally efficient method to model how terrain affects communications signals and other electromagnetic waves and is working with NRAO engineers to validate and improve the model.

The EMIL models integrate along the whole path instead of just working with certain data points, as done in commercially available models. The data is still only taken at certain locations, but generating a set of random curves to connect those points introduces error from which they can generate a standard deviation.

“We’ve got the topographical modeling down, now we’re working on incorporating the electrical conductivity of the soil,” he says. “It turns out that the earth is not a perfect conductor, which must also be taken into account for predicting the behavior of radio waves.”

Brown and his team have been taking measurements at Green Bank and in the surrounding area to validate their model. “We aren’t trying to fit the existing data,” he explains, “but see how the new models compare to the old. We want to be able to accurately predict a signal from point A to point B.”

Policing the quiet zone isn’t the only application of the new propagation research. Naval vessels moving in the littoral zone, where the land meets ocean would also benefit from knowing how signals are traveling across land, he says. Another application would be for cognitive and smart radios; if they could predict the necessary signal level, they could conserve power.

The effort is funded by the Naval Surface Warfare Center, the NRAO, and the Army Research Office.